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bpf: add specification for BTF Var and DataSec kinds

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This adds the BTF specification and UAPI bits for supporting BTF Var
and DataSec kinds. This is following LLVM upstream commit ac4082b77e07
("[BPF] Add BTF Var and DataSec Support") which has been merged recently.
Var itself is for describing a global variable and DataSec to describe
ELF sections e.g. data/bss/rodata sections that hold one or multiple
global variables.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2019-04-09 23:20:08 +02:00 committed by Alexei Starovoitov
parent 3e0ddc4f3f
commit f063c889c9
2 changed files with 85 additions and 4 deletions
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57
Documentation/bpf/btf.rst
View File

@ -82,6 +82,8 @@ sequentially and type id is assigned to each recognized type starting from id
#define BTF_KIND_RESTRICT 11 /* Restrict */
#define BTF_KIND_FUNC 12 /* Function */
#define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
#define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */
Note that the type section encodes debug info, not just pure types.
``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
@ -393,6 +395,61 @@ refers to parameter type.
If the function has variable arguments, the last parameter is encoded with
``name_off = 0`` and ``type = 0``.
2.2.14 BTF_KIND_VAR
~~~~~~~~~~~~~~~~~~~
``struct btf_type`` encoding requirement:
* ``name_off``: offset to a valid C identifier
* ``info.kind_flag``: 0
* ``info.kind``: BTF_KIND_VAR
* ``info.vlen``: 0
* ``type``: the type of the variable
``btf_type`` is followed by a single ``struct btf_variable`` with the
following data::
struct btf_var {
__u32 linkage;
};
``struct btf_var`` encoding:
* ``linkage``: currently only static variable 0, or globally allocated
variable in ELF sections 1
Not all type of global variables are supported by LLVM at this point.
The following is currently available:
* static variables with or without section attributes
* global variables with section attributes
The latter is for future extraction of map key/value type id's from a
map definition.
2.2.15 BTF_KIND_DATASEC
~~~~~~~~~~~~~~~~~~~~~~~
``struct btf_type`` encoding requirement:
* ``name_off``: offset to a valid name associated with a variable or
one of .data/.bss/.rodata
* ``info.kind_flag``: 0
* ``info.kind``: BTF_KIND_DATASEC
* ``info.vlen``: # of variables
* ``size``: total section size in bytes (0 at compilation time, patched
to actual size by BPF loaders such as libbpf)
``btf_type`` is followed by ``info.vlen`` number of ``struct btf_var_secinfo``.::
struct btf_var_secinfo {
__u32 type;
__u32 offset;
__u32 size;
};
``struct btf_var_secinfo`` encoding:
* ``type``: the type of the BTF_KIND_VAR variable
* ``offset``: the in-section offset of the variable
* ``size``: the size of the variable in bytes
3. BTF Kernel API
*****************

32
include/uapi/linux/btf.h
View File

@ -39,11 +39,11 @@ struct btf_type {
* struct, union and fwd
*/
__u32 info;
/* "size" is used by INT, ENUM, STRUCT and UNION.
/* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC.
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
* FUNC and FUNC_PROTO.
* FUNC, FUNC_PROTO and VAR.
* "type" is a type_id referring to another type.
*/
union {
@ -70,8 +70,10 @@ struct btf_type {
#define BTF_KIND_RESTRICT 11 /* Restrict */
#define BTF_KIND_FUNC 12 /* Function */
#define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
#define BTF_KIND_MAX 13
#define NR_BTF_KINDS 14
#define BTF_KIND_VAR 14 /* Variable */
#define BTF_KIND_DATASEC 15 /* Section */
#define BTF_KIND_MAX BTF_KIND_DATASEC
#define NR_BTF_KINDS (BTF_KIND_MAX + 1)
/* For some specific BTF_KIND, "struct btf_type" is immediately
* followed by extra data.
@ -138,4 +140,26 @@ struct btf_param {
__u32 type;
};
enum {
BTF_VAR_STATIC = 0,
BTF_VAR_GLOBAL_ALLOCATED,
};
/* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
* additional information related to the variable such as its linkage.
*/
struct btf_var {
__u32 linkage;
};
/* BTF_KIND_DATASEC is followed by multiple "struct btf_var_secinfo"
* to describe all BTF_KIND_VAR types it contains along with it's
* in-section offset as well as size.
*/
struct btf_var_secinfo {
__u32 type;
__u32 offset;
__u32 size;
};
#endif /* _UAPI__LINUX_BTF_H__ */